Field of the Invention
The present invention relates to an image reading apparatus and an image forming system.
Description of Related Art
In the past, there is a system in which a nip portion of a conveyance roller is released in accordance with the thickness of a sheet which is conveyed by the conveyance roller (for example, refer to Japanese Patent Published Application No. 2014-177335).
The prior art technique described in this Published Application makes it possible to inhibit occurrence of sheet conveyance troubles by releasing a nip portion of a conveyance roller in accordance with the thickness of a sheet.
However, in the case where the prior art technique described in the Published Application is applied when reading an image formed on a sheet which is passed between a scanner and a calibration member, the sheet may move outside the area in which the reading performance of the scanner is guaranteed, depending upon the stiffness of the sheet.
For example, if the sheet is passed through a gap without pressing in accordance with the technique described in the Published Application even though the stiffness of the sheet is small, the sheet passed between the scanner and the calibration member substantially flaps in the reading position of the scanner as the conveying speed of the sheet increases. On the other hand, in the case where a sheet passing through a gap is pressed when reading an image formed on the sheet unlike in accordance with the prior art technique described in the Published Application, the occurrence frequency of conveyance troubles of the sheet passed between the scanner and the calibration member may increase as the stiffness of the sheet increases.
Accordingly, in accordance with this prior art technique, while the occurrence frequency of conveyance troubles of a medium such as a sheet can be inhibited, it is impossible to inhibit the medium from flapping in the reading position of the scanner so that an image formed on the medium may not correctly be read.
The present invention is made in order to solve such a prior art problem and it is an object of the present invention to provide an image reading apparatus and an image forming system in which it is possible to decrease the occurrence frequency of conveyance troubles of a medium and correctly read the image formed on the medium.